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Dear Profs. Blaha and Marks,<br>
<br>
Thank you for your comments, it helps.<br>
<br>
I indeed made a mistake of starting with asymmetric slab - first I
did Fe atom only on one side of MgO, relaxed it, and then added
another Fe atom on the other side of MgO. When starting with
symmetric Fe/MgO/Fe slab things behave as expected. I wanted to
check if there is much difference between having Fe atom on one or
on both sides of the slab.<br>
<br>
I am still using iMac computer with i7-3770 and 16 GB of RAM
(perhaps I should really move to the cluster...), and my new
external hard drive was not formatted to see case sensitive file
names (Mac operating system allows things like this!). This is why I
had issues with case.inm and case.inM filenames but it is fixed now.<br>
<br>
For now I am happy with structure relaxation results and I like how
it is done with MSR1a. On iMac I cannot really do much more than 6-8
monolayer slab (I want to calculate dense k-point mesh later), but I
think it will be sufficient for my purpose (I am currently checking
if there is much difference between different slab thicknesses).<br>
<br>
Best,<br>
Lukasz<br>
<br>
<br>
<div class="moz-cite-prefix">On 6/1/2018 1:16 PM, Lukasz Plucinski
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:4c328fd5-e9e2-d33f-ac1e-41b1bdac8b2d@fz-juelich.de">
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<th nowrap="nowrap" valign="BASELINE" align="RIGHT">Subject:
</th>
<td>Re: [Wien] Structure optimization</td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE" align="RIGHT">Date:
</th>
<td>Sat, 19 May 2018 09:06:33 -0500</td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE" align="RIGHT">From:
</th>
<td>Laurence Marks <a class="moz-txt-link-rfc2396E"
href="mailto:L-marks@northwestern.edu"
moz-do-not-send="true"><L-marks@northwestern.edu></a></td>
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<th nowrap="nowrap" valign="BASELINE" align="RIGHT">Reply-To:
</th>
<td>A Mailing list for WIEN2k users <a
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<th nowrap="nowrap" valign="BASELINE" align="RIGHT">To: </th>
<td>A Mailing list for WIEN2k users <a
class="moz-txt-link-rfc2396E"
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<br>
<br>
<div dir="ltr">It works...but (sorry Peter) it can be bad
science. There are special cases where it is appropriate, but
it can also be very inappropriate.
<div><br>
</div>
<div>There is a long history of people fixing some atomic
positions to bulk positions when performing surface
calculations. However, the strain field of any surface
decays exponentially in the selvedge layer, and removing
this can be very wrong. For instance, there are many known
cases where the surface induces a ferroelectric distortion
which fixed positions will prevent from happening. The
rigorous method is to check that the atomic positions in the
center of the slab are "close enough" to those in the bulk.
If they are not then either the slab needs to be thicker or
there has been a surface induced phase transition.</div>
<div><br>
</div>
<div>And, fixing positions for a surface <i
style="font-weight:bold">in general does not improve the
convergence</i>. If you are lucky it will, but not in
general. The reason (as I have mentioned before) is that the
convergence scales with the number and width of the
eigenvalue clusters, not the number of variables. If the
convergence of Wien2k and other DFT codes scaled with the
number of density variables, the methods would be useless!
DFT is a useful method because it will typically converge in
10-100 scf iterations because there are only a few
eigenvector clusters of the dielectric response (in density
only calculations) and the force matrix (with PORT). MSR1a
is typically efficient because the number and width of the
clusters of the general dielectric response with both
density and electronic terms included is smaller than the
product of the clusters for the electronic and atomic
components.</div>
<div><br>
</div>
<div>Sorry for being so pedantic...but rigor matters.</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sat, May 19, 2018 at 7:56 AM,
Peter Blaha <span dir="ltr"><<a
href="mailto:pblaha@theochem.tuwien.ac.at"
target="_blank" moz-do-not-send="true">pblaha@theochem.tuwien.ac.at</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex"><span
class="">> - How can I lock some atoms in position
during structure optimization?<br>
<br>
</span>In case.inM put the 1.0 values of x,y and/or z of
the corresponding <br>
atom (line) to 0.0.<br>
<br>
It works well. We do it all the time....<br>
<br>
> <br>
> Best,<br>
> Lukasz<br>
> <br>
<br>
-- <br>
------------------------------<wbr>------------------------------<wbr>--------------<br>
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna,
A-1060 Vienna<br>
Phone: +43-1-58801-165300 FAX:
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<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr"><span
style="font-size:12.8px">Professor
Laurence Marks</span><br>
</div>
<div dir="ltr"><span
style="font-size:12.8px">"Research is to
see what everybody else has seen, and to
think what nobody else has thought", </span><span
style="font-size:12.8px">Albert
Szent-Gyorgi</span><br>
<a
href="http://www.numis.northwestern.edu"
target="_blank" moz-do-not-send="true">www.numis.northwestern.edu</a> ; <span
style="font-size:12.8px">Corrosion in
4D: </span><a
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<div><span style="font-size:12.8px">Partner
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<div>Co-Editor, Acta Cryst A</div>
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